1. Field of the Invention
The present invention relates to an image reading apparatus and an image reading method, and particularly to an image reading apparatus for optically reading an image from an original using an ADF (Automatic Document Feeding) unit and an image reading method.
2. Description of the Related Art
There is conventionally known an apparatus that detects opening/closing of an automatic document feeding unit (to be referred to as an ADF unit hereinafter) from the feature amount of a pattern image obtained by reading an ADF unit opening/closing detection mark by an image reading unit, like an image reading apparatus disclosed in FIG. 1 of Japanese Patent Laid-Open No. 2010-278563.
According to Japanese Patent Laid-Open No. 2010-278563, the lengths of read images of opening/closing detection marks M arranged at two points, that is, on the rear side close to the rotation shaft of the ADF unit and on the front side far from the rotation shaft are compared, thereby determining opening/closing of the ADF unit. This arrangement is disclosed in paragraph 0078 and FIGS. 3, 7, and 8 of Japanese Patent Laid-Open No. 2010-278563.
According to Japanese Patent Laid-Open No. 2010-278563, the density differences between read images of opening/closing detection marks M arranged at two points, that is, on the rear side close to the rotation shaft of the ADF unit and on the front side far from the rotation shaft and their peripheral portions are compared, thereby determining opening/closing of the ADF unit. This arrangement is disclosed in paragraphs 0095 to 0097 and FIG. 10 of Japanese Patent Laid-Open No. 2010-278563.
In the arrangement according to Japanese Patent Laid-Open No. 2010-278563 which compares the lengths of read images of the opening/closing detection marks M, however, if the influence of outside light that enters from the left side shown in FIG. 3 with respect to the light source is large, the length difference between the mark M on the rear side close to the rotation shaft of the ADF unit and that on the front side far from the rotation shaft becomes small. Hence, the detection accuracy may lower due to the influence of outside light.
Additionally, in Japanese Patent Laid-Open No. 2010-278563, if the influence of outside light that enters from the front side to the rear side of FIG. 10 with respect to the light source is large, the difference between the density difference between the mark M and its peripheral portion on the rear side close to the rotation shaft of the ADF unit and that on the front side far from the rotation shaft becomes small, and the detection accuracy may lower. At any rate, the influence of outside light affects the accuracy of determining the opening/closing of the ADF unit.